1d Runs over northern and southern tack . H/r?e?s. Ans is harness , an item of horse tack, as confirmed by https://www.theanswerbank.co.uk/Quizzes-and-Puzzles/Crosswords/Question1617760.html however I can't see how it parses.
Harness has a n for northern and a s for southern and a r for runs but that still leaves h a e s. No doubt very obvious but can't see it. Thanks .